linux-kernel - Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

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Message-ID: <20101118200807.GC8131@redhat.com>
Date:	Thu, 18 Nov 2010 15:08:07 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Robert Richter <robert.richter@....com>, ying.huang@...el.com,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

On Thu, Nov 18, 2010 at 01:51:44PM -0600, Jason Wessel wrote:
> > So the problem is when the nmi watchdog is enabled, the perf event is
> > 'active' and thus tries to read the counter value.  Because it is always
> > zero, perf just assumes the counter overflowed and the NMI is his.
> >
> > Not sure how to fix it yet, other than include the logic that detects we
> > are on a guest and disable perf??
> >
> >   
> 
> I highly doubt we want to disable perf.   I would rather use the source
> and fix the nmi emulation in KVM/Qemu after we hear back the results

Well I think Peter does not have a positive opinion about emulating perf
inside a guest.  Nor are the KVM folks having much success in doing so.

Just to clarify, perf counter emulation is _not_ implemented in kvm.
Therefore disabling perf in the guest makes sense until someone gets
around to actually writing the emulation code for perf in a guest. :-)

Cheers,
Don
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